For a good laundry softener mix 2 cups of white vinegar with 2 cups of baking soda and 2 cups of water. Combine the ingredients carefully over a sink because the soda and vinegar will effervesce. Pour the mixture into a plastic bottle. You can use an old laundry softener bottle since they have measuring cups that are used as caps. Use 1/4 cup in the final rinse of your washer cycle.
DO NOT USE VINEGAR IF YOU ADD CHLORINE BLEACH TO YOUR RINSE WATER. IT WILL PRODUCE HARMFUL VAPORS.